Created through a process known as blow molding, plastic bottles are one of the most commonly used beverage containers in the modern world. Using this process, plastic bottle manufacturers are able to use a variety of plastic materials to manufacture bottles in a wide variety of shapes and sizes. Typically, however, most plastic bottles are characterized by thin wall construction, comparably small sizes, light weight and low costs.
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Extrusion Blow Molding Bottles
Plastic bottle manufacturers create virtually all of their products the same way, using a type of blow molding known as extrusion blow molding. To start this process, manufacturers load a hopper with stock, which is a collection of small, raw thermoplastic pellets or fibers. From the hopper, they point the stock towards and direct it into a conveyance channel in which resides a large screw. As it turns, this large screw pressures the stock and pushes it towards a mold cavity simultaneously. With the added influence of heating elements in the channel, the stock becomes liquefied. Once liquefied, the plastic is forced into a mold cavity, where it takes on its shape. Manufacturers then force compressed air into the mold cavity, where the partially formed plastic product still sits. The purpose of the compressed air is to render the plastic product hollow and hold it against the body of the mold until it once again takes on its shape. After this, the newly formed plastic bottle is permitted to cool and harden before it is removed from the mold. From here, the product can be checked for imperfections and shipped, or sent on for secondary processing. Sometimes, plastic bottle manufacturers use the methods of injection blow molding (IBM) or injection stretch blow molding to make plastic bottles.
Stages of Injection Blow Molding
Injection blow molding (IBM) is performed in three major stages: injection, blowing and ejection.
- Injection Stage
- During the first stage, a molten polymer is fed into a hot runner manifold and injected via nozzles into a heated cavity and onto a core pin. The polymer surrounding the core pin adapts the shape of the cavity, forming an exterior, while the core pin ensures that it does not become solid, but rather remains hollow.
- Blow Molding Stage
- During the second stage, this pin rotates its way to a blow molding station, where the mold is clamped around a core rod, inflated inside a preform and then cooled.
- Ejection Stage
- During the third stage, once the plastic form has hardened, the finished product is moved into the ejection position and stripped off the core rod.
- It is important to note that this type of blow molding is the least commonly chosen method of all the plastic blow molding processes for plastic bottle manufacturing. Rather, it is only used to make small capacity bottles and jars. Also, manufacturers using this method cannot add handles or increase bottle barrier strength. Next, injection stretch blow molding is used to create rectangular, cylindrical and oval bottles. Injection stretch blow molding can be carried out using one of two methods: single-stage or two-stage. In the first method, both the preform and the bottle are blown in the same machine. In the second method, the preforms are created first, using the injection molding process, then they are later reheated and stretched into their intended shape and size. The latter step is done using pressurized air and core rods, which help the preforms stretch properly.
Types of Materials Used in Plastic Bottles
To make their products, plastic bottle manufacturers use a number of different plastics, such as polyethylene, polyethylene terephthalate (PET) and polypropylene. They may use raw stock that has been newly made, or they may use plastic materials that have come from reprocessed and recycled products. The use of recycled materials helps manufacturers reduce their carbon footprint, as many plastics pose a threat to the environment if not recycled. Along these same lines, in addition to manufacturing the bottles themselves, many plastic bottle manufacturers are also able to prepare used plastic bottles for use as recycled material in a breathtaking number of applications, particularly in the auto industry. There, plastic bottles repurposed as industrial yarn can be weaved into fabric suitable for the construction of sound absorbers, upholstery and panels. Current estimates say that it takes about 40 recycled plastic bottles to construct the seat of a car. Reusing plastic bottles is an excellent endeavor not only because it is good for the environment, nor just because doing so helps manufacturers obey laws regarding recycling, but because it is lucrative; the demand for recycled plastic products is high and the cost to make them is low. On top of all of this, plastic bottle manufacturers continue to strive to find biodegradable plastic solutions, to ensure that the world around them is able to thrive just as well as their business.